1. Field of the Invention
This invention relates to a power transmission apparatus comprising two control systems for transmitting power to the power shaft connected to a load shaft, one of the two systems being an automatic control system for transmitting power from a motor and the other being a manual control system for manually transmitting power, wherein the power transmission through the manual control system precedes that through the automatic control system and the power transmission through said manual control system can be automatically switched, when it is stopped, to that through the automatic control system.
2. Description of the Prior Art
Most of the conventional apparatus of this type are provided with automatic-manual switching mechanisms for determining whether to transmit the power to the power shaft either through the automatic control system or through manual control system. However, the apparatus provided with such automatic-manual switching mechanisms are likely to result in mis-switching action by an unexpected external force applied thereto. In order to prevent the accidents that may be caused by such mis-switching operations, a power transmission apparatus has been proposed which transmits the power to the power shaft through either of the automatic or manual control without utilizing the automatic-manual switching mechanisms (for instance, Japanese Pat. No. 605,743). Such apparatus, however, have extremely complicated structures, require high accuracy in the fabrication and are, consequently, expensive.